1. Field of the Invention
The invention relates generally to surgical methods and apparatus for clamping cables or wires. More particularly, the invention relates to methods and apparatus for clamping cables, wires or other elongate members used in orthopedic surgical techniques.
2. Description of the Prior Art
Surgical cables and wires are now used extensively in orthopedic surgery for securing bones and bone fragments in place and for fastening surgical implements to bones. Typically, surgical cables are implanted using tensioning devices, which apply tension to a cable looped around the bone, and crimps that are deformed to clamp the cable loop in place.
The prior art is typified by U.S. Pat. No. 5,395,375 to Miller et al, the entire writing of which is incorporated herein by reference. The disclosed technique involves the use of a small lever-action cable clamp located along the cable between the crimp and the tensioning tool. A first cable may be provided with a pre-final amount of tension and then the cable clamp operated to secure the first cable in the pre-final position. The tensioning tool may then be removed from the first cable and used in conjunction with another cable clamp, to apply tension to a second cable. This technique permits the readjustment of the tension on the cables used in an orthopedic application.
Cable clamps like of the prior art incorporate a cam lever that bears directly on the cable surface. Thus, as the cam lever is operated to clamp the cable, the clamping force is applied to a relatively small area of the cable surface and the cable is subjected to potentially damaging shear and compressive forces. This may result in local weakening of the cable, which is undesirable especially since the cable may be in place for long periods of time and subject to repetitive stresses and any weakened portion will represent the potential for failure of the cable. It would therefore be desirable to provide an improved cable clamp that can be used to temporarily clamp a cable without subjecting the cable to potentially damaging localized stresses.
Another problem with cable clamps of the prior art is that they do not provide for efficient and risk-free operation with a variety of different sized cables. Different sized cables are employed in surgical operations, depending on the particular application. Cable clamps like the one disclosed by Miller and described above, are configured to have only an open and closed position, with the closed position applying the maximum clamping force to the cable. When used with larger cable diameters, prior art devices may apply excessive and damaging forces to the cable when the cam is moved to the clamping position. It would therefore be desirable to provide a cable clamping device having a single design that may be used to efficiently and safely clamp cables having different diameters or lateral dimension.
Yet another shortcoming of prior art cable clamps is that they do not provide stable locking positions or positive indication to a surgeon as to when suitable clamping force has been applied to the clamped cable. For example, prior art devices like the one described by Miller use a cam lever having a smooth cam surface without predefined locking positions. Thus, a physician must rely only on the tactile sensation of continuously increasing forces applied to the cam lever to determine when sufficient clamping force is applied to the cable. It would therefore be desirable to provide a cable clamp which has at least one pre-defined locking position and which provides a positive tactile indication to a surgeon that sufficient yet safe clamping force has been applied to the clamped cable. It would further be desirable to provide such stable locking positions and positive tactile indication for more than one size of cable to be used with the cable clamp.
The aforementioned problems are addressed by the present invention, which in a preferred embodiment, provides a clamping device that incorporates a cable housing having a cable bore defined therein and cam operated saddle member adapted to move with respect to the housing. The saddle member is actuated by a cam lever which is provided with a cam surface that engages the cable housing. In a preferred embodiment, the cam lever is movably secured to the saddle member by a pivot pin. Movement of the cam lever results in movement of the saddle member in a direction that is generally transverse to the cable bore. Since the cam surface does not act directly on the cable surface and since the saddle member applies force in a direction that is generally transverse to the cable, the cable may be clamped in a safe and efficient manner without potentially damaging compressive or shear forces being applied.
According to another aspect of the invention, the clamping device is provided with at least one locking jaw that is adapted to redirect the cable and enhance the clamping capability. In a preferred embodiment, the locking jaw is provided with an undulating surface and is fastened to the saddle member so as to redirect the cable from a substantially straight path to a non-straight, for example, undulating or serpentine path when the saddle member is moved to a clamping position. In another embodiment, both the saddle member and the housing are provided with cooperating jaws that define a non-straight, for example, undulating or serpentine path, when the saddle member is in a clamping position. Since the cable is redirected to a non-straight path, the clamping forces is distributed to a greater surface area of the cable, thereby reducing the potential for damaging localized stress concentrations and reducing the normal force necessary to safely clamp the cable.
According to yet another aspect of the invention, the clamping device is provided with a cam having a plurality of locking positions that enable a surgeon to determine by a positive tactile indication that sufficient clamping force has been applied to the cable. In a preferred embodiment, the locking positions are defined by facets on the cam surface, which may be flattened portions. The dimensions of the facets are selected based on the lateral dimensions of different-sized cables or wires that are to be used with the clamping device. Thus, as the cam lever is rotated to a pre-defined locking position, the surgeon is given a tactile indication as to when the cam lever is in one of its pre-defined locking positions.